In order to increase safety in traffic active as well as passive systems for further improving safety in traffic are continuously developed. Passive safety systems are directed toward reducing the effect of an accident, in the event an accident takes place while active safety systems are directed toward reducing the probability of occurrence of accidents. One type of active safety systems are collision avoidance systems relying on sensor technology for estimating a traffic situation. In this type of systems sensors are used to detect the presence of objects in a future trajectory of the vehicle. In the event the system detects that an object is within a future trajectory of the vehicle, normally a warning sign is produced to alert the driver. Systems that intercept the control of the vehicle, such as by braking the vehicle are also known.
In most known collision avoidance systems and methods, future trajectories of all detected object are estimated and compared with the future trajectory of the vehicle. In the event the future trajectory of an object coincides with the future trajectory of the vehicle, a conflict event is detected. The future trajectories of the detected objects are based on position and velocity of the objects. Normally position and velocity are detected by use of sensors such as radars. In order to separate between large and small objects, between objects made of metal from concrete or animals object recognition based on input signals from cameras may be used. As soon as the velocity and position has been detected by the radar, and it has been verified that the detected object is a potentially dangerous object, and not for instance a flying insect or paper litter whirling round, the future trajectory of the object is estimated primarily from input data relating to the position and velocity of the object in question. However, the future trajectory of the object may drastically change due to influence from other objects on the road. In the article, “Monte Carlo Road Safety Reasoning”, Broadhurst, A., Baker, S., Kanade, T. Monte Carlo road safety reasoning, Proceedings of the IEEE Intelligent Vehicles Symposium 2005, 6-8 Jun. 2005, Page(s): 319-324, Las Vegas, Nev., USA, a method is disclosed in which the future trajectory of an object is influenced by the traffic situation, that is by the future trajectories of other objects present on the road. The invention relates to a system and method for collision avoidance wherein the future trajectories of external objects are influenced by the traffic situation. In the Broadhurst article the following use of the system in the host vehicle is suggested: closed loop control of the vehicle for selecting the best predicted action, display of the best action to take in order to advice the driver, or display of warning signs for objects or unsafe regions of the road. However, in the event the control system suggested in this article is used to intercept in the control of the host vehicle by using the best predicted action for control of the host vehicle, the host vehicle will be run by an autopilot. Such solutions are generally not accepted for legal reasons and are furthermore mot appreciated by drivers. Even though the system and method described in, “Monte Carlo Road Safety Reasoning” has contributed with an important advance in object tracing and future path determination, there is still a need for improvements as regards the use of the information generated by the future trajectory estimator.